The present invention provides a process for the photopolymerization of vinyl compounds in the presence of a photoinitiator.
Photopolymerization has many useful applications in the technical field as, for example, for the curing of lacquers and coatings, in the manufacture of printing plates and in letter press printing.
Photopolymerization is also useful in the dental field as well. Photopolymerizable materials are used in the preparation of dental fillings and sealings, of crowns and bridges and artificial teeth and dentures see, for example, British Pat. No. 569,974 and German Patent Publications Nos. 23 15 645, 23 57 324, 29 10 077 and 29 14 537).
British Pat. No. 1,408,265 describes photopolymerizable materials which contain as a photoinitiator a mixture of:
(a) at least one photosensitizer of the formula ##STR3## where X is CO, C(R.sup.1)(R.sup.2) or C(R.sup.3)(OR.sup.4), R.sup.1,R.sup.2,R.sup.3,R.sup.4, which may be the same or different, are hydrogen or hydrocarbyl groups, n is 0 or 1, and the groups A, which may be the same or different, are hydrocarbyl or substituted hydrocarbyl groups and in which the groups A may be further linked together by a direct link or by a divalent hydrocarbyl group, or in which the groups A together may form a fused aromatic ring system, the groups A being aromatic or substituted aromatic (1) when n is 1 and X is C(R.sup.1)(R.sup.2) and (2) when n is 0, and
(b) at least one reducing agent capable of reducing the photosensitizer when the photosensitizer is in an excited state and having the structure ##STR4## where M is an element of Group V B of the Periodic Table and the units R, which may be the same or different, are hydrogen atoms, hydrocarbyl groups, substituted hydrocarbyl groups or groups in which two units R together with the element M form a cyclic ring system, no more than two of the units R being hydrogen atoms or substituted hydrocarbyl groups and, where element M is attached directly to an aromatic group R, at least one of the other units R has a ##STR5## group attached to M.
British Pat. No. 1,465,897 discloses photopolymerizable materials useful in dentistry which contain as a photoinitiator a mixture of:
(a) at least one photosensitzer of the formula ##STR6## in which the groups A, which may be the same or different, are hydrocarbyl groups or substituted hydrocarbyl groups; and
(b) at least one reducing agent capable of reducing the photosensitizer when the photosensitizer is in an excited state and having the formula ##STR7## wherein M is an element of Group Vb of the Periodic Table and the units R, which may be the same or different, are hydrogen atoms, hydrocarbyl groups, substituted hydrocarbyl groups, or groups in which two units R together with the element M form a cyclic ring system, no more than two of the units R being hydrogen atoms and the element M not being attached directly to an aromatic group.
The resulting mixtures can be cured by exposure to visible light or through ultraviolet rays. Examples of the photosensitizers include benzil, p,p'-dimethoxy benzil, benzoin, and camphorquinone. Reducing agents include propylamine, dimethylaminoethyl methacrylate, N,N'-dimethylaniline and piperidine.
It is the object of the present invention to provide a photoinitiator having (a) at least one photosensitizer, and (b) at least one reducing agent for the photopolymerization of vinyl compounds which effects a rapid curing and results in good color fastness of the polymerized substance.